Variable displacement pumps of the triple-gear type



Feb. 2, 1965 e. WIGGERMANN VARIABLE DISPLACEMENT PUMPS OF THE TRIPLE-GEAR TYPE 5 Sheets-Sheet 1 Filed 001:. 21, 1960 Feb. 2, 1965 s. WIGGERMANN VARIABLE DISPLACEMENT PUMPS OF THE TRIPLE-GEAR TYPE 5 Sheets-Sheet 2 Fiied Oct. 21, 1960 Feb. 2, 1965 G. WIGGERMANN ,1

VARIABLE DISPLACEMENT PUMPS OF THE TRIPLE-GEAR TYPE Filed Oct. 21, 1960 s Sheets-Sheet s uON Feb. 2, 1965 VARIABLE DISPLACEMENT PUMPS OF THE TRIPLE-GEAR TYPE Filed Oct. 21, 1960 FIG. HQ

G/WIGGERMANN 3,168,043

5 Sheets-Sheet 4 FIG.8

Feb. 2, 1965 e. WIGGERMANN 3,168,043

VARIABLE DISPLACEMENT PUMPS OF THE TRIPLE-GEAR TYPE Filed Oct. 21, 1960 5 Sheets-Sheet 5 FIG. l3

GEAR 4 United States Patent 3,168,043 VARIABLE DISPLACEMENT PUMPS 01* THE TRIPLE-GEAR TYPE Georg Wiggcrmann, Kressbronn, Germany, assignor to Reiners Wiggermann Getriebeund Maschincnhau,

Kressbronn, Germany, a corporation of Germany Filed Oct. 21, I960, Ser. No. 64,199 It) (Ilaims. (Cl. 103-429) My invention relates to positive-displacement hydraulic machines of the controllable type in which a train of at least three intermeshing spur gears is mounted in a sealed housing and the intermediate one of the three spur gears is radially displaceable so that the spacing of its rotational axis from the corresponding axes of the respective two adjacent gears can be varied continuously for varying the delivery of the machine. In a more particular aspect, my invention concerns improvements in a housing structure for such machines.

The invention will be hereinafter described in terms of a pump, although it is also applicable to hydraulic motors.

In theory, controllable gear pumps of the type described above afford the possibility of a continuous variation in volumetric delivery from zero up to a maximum in each desired direction of delivery. Their design, in principle, is rather simple and their reliability and ruggedness should be akin to the corresponding properties of conventional gear-type pumps having a fixed spacing between the gear axes and a fixed quantitative delivery for a given speed of gear rotation.

Despite these theoretical-1y attainable qualities of triplegear pumps, however, they have not yet found appreciable use in practice because they also possess peculiar disadvantages which, in the pump designs heretofore contemplated, outweigh the above-mentioned advantages.

(A) In the first place, the triple-gear controllable pumps as heretofore known require large overall dimensions and a correspondingly great weight in comparison with other types of pumps of the same power output. In a triple-gear pump, the gears for a desired quantitative delivery can be reduced in size by employing a special tooth design, and this tends to facilitate correspondingly reducing the overall dimensions of the pump. However, there still remains the problem of devising a housing capable of withstanding the occurring stresses so that advantage can be taken of the favorable gear-tooth design toward greatly reducing the over-all dimensions as well as the total weight of the machine.

(B) Another disadvantageous feature of the triplegear controllable pumps is the fact that the separation of the suction chamber from the pressure chamber involves very long sealing gaps. If this is not taken into account in the design of the pump housing, a high degree of internal leakage and hence a great impairment of the volumetric efiiciency are encountered. Another problem to be solved is therefore how to devise a housing which virtually does not breathe under the alternating internal pressures, but is so tight and rigid in the direction of the gear axes that, even at high internal pressure, no appreciable enlargement of sealing gaps between the gears and the housing walls can occur.

(C) Due to the long sealing gaps of prior-art pumps, a controllable triple-gear pump possesses relatively large mutually engaging surfaces which, during operation, move relative to each other; and a reduction of the gap width for the purpose of improving internal sealing has the effect of greatly increasing the internal frictional losses so that the mechanical efficieney of the pump is impaired. Consequently, it is another problem how to devise a construction which satisfactorily meets the requirement 3,168,043 Ia'tented Feb. 2, 1955 for a narrow sealing gap width as well as for low internal friction.

(D) Another shortcoming of the controllable triplegear pumps heretofore known is their internal rotation of the hydraulic medium which involves hydraulic eddycurrent losses and hence also impairs the efficiency, aside from causing appreciable heating up of the hydraulic medium. It is therefore a further problem to devise a pump-housing construction which satisfactorily copes with the just-mentioned internal flow conditions.

(E) Prior controllable triple-gear pumps tend to produce an extremely dlisagreeable noise similar to that of a siren. This virtually excludes using such pumps for many purposes. It is therefore also a problem to find a pump design which permits minimizing the noise generated to an acceptable magnitude.

It is among the objects of my invention to improve controllable triple-gear pumps, and particularly the pump housing thereof, so as to solve one or more of the abovernentioned problems, and to provide a novel triple-gear controllable displacement machine advantageously applicable in practice and equivalent or superior to other types of pumps with respect to performance and other operating characteristics.

The features of my invention by virtue of which these objects are attained, sa-id features being set (forth with particularity in the claims annexed hereto, will be described presently with reference to the embodiments of triple-gear pumps according to the invention illustrated by way of example on the accompanying drawings in which:

FIG. 1 is a partly sectional front view of a first embodiment of the invention, the section being taken along the line II in FIG. 2.

FIG. 2 is a sectional view along the line IIII in FIG. 1.

FIG. 3 is a front view of another embodiment.

FIG. 4 shows another front view of the embodiment according to FIG. 3, but with a portion of the pump housing removed.

FIG. 5 is a section along the line VV in FIG. 3.

FIG. 6 is a section through the pump housing along the line VI-VI in FIG. 3.

FIG. 7 shows a sectional view along the line VIIVII in FIG. 3.

FIG. 8 shows a sectional view of a duct member applicable in lieu of those illustrated in FIGS. 3 and 5.

FIG. 9 is a cross section along the line IX-IX in FIG. 8.

FIG. 10 illustrates a modification of the duct members in a sectional view corresponding, as to its position and representation, to the sectional view presented in FIG. 7.

FIG. 11 is a cross section through the housing along the line XI-XI in FIG. 4.

FIGS. 12 and 13 are respective explanatory diagrams relating to the meshing conditions of the spur gears in the pump.

For a detailed description of the general design and op erating principles as well as a favorable tooth configuration of the spur gears in the pump, reference may be had to my copending application Serial No. 701,764, filed December 10, 1957. The present application is also related to my copending application Serial No. 57,797 filed September 22, 1960, for a hydraulic gear type machine of controllable displacement. However, before describing the present invention proper, a brief description of the fundamental pump components and their operation will be given with reference to FIGS. 1 and 2 of the accompanying drawings. A pump housing, shown composed of two parts 1a and 1b, encloses a train of three spur gears 2, 3, 4 on respective shafts 6, 9 and 17, whose rotational axes are parallel to each other. The shaft 6 of the outer gear 2 is driven from a motor or other source of mechanical power. The driving shaft 6 as well as the shaft 17 of the other outer gear 4 have fixed axes relative to the pump housing. The central gear 3, however, is journalled on an eccentric portion 9a which is normally stationary and forms part of theshaft 9. Turning the shaft 9 by means of a control arm 8a to a different angular position'causes the eccentric 9a to shift the central gear 3 along the center axis X (FIG. 1) of the pump toward one of the outer gears and away from the other.

The housing surrounds the three gears so as to leave clearance spaces at both sides of the central gear 3. These spaces form pressure, and suction chambers and communicate with respective ducts 7a and 7b through which the hydraulic medium, preferably oil, passes through the pump. The amount of delivery from the inlet duct to the outlet duct through the meshing gear teeth of the central gear and one of the outer gears is dependent upon the selected axialspacing of the central gear from the active outer gear. When the central gear is in midposition, i.e. equally spaced from the respective axes of the two outer gears 2 and 4, the delivery of the pump, regardless of its operating speed, is zero. When the control arm 8a is shifted from the zero position toward one side, the delivery of the pump is increased in one direction. When the control arm 8a is shifted to the other side, the delivery is correspondingly increased in the other direction.

As far as described, the features of a triple-gear pump of controllable delivery are known as such or were previously disclosed, for example in the above-mentioned copending applications. The improvements of such pumps in accordance with my present'invention will be described presently.

In the foregoing portion A of this specification, the problem is mentioned to devise a triple-gear pump housing of smallest possible dimensions and smallest attainable weight. This requires minimizing as much as possible the internal housing surfaces exposed to the delivering pressure, because this results in greatly reducing the effects of forces and stresses to which the housing is subjected.

To this end, and in accordance with a feature of my invention, the three bearings of the housing for journalling the respective spur gears are so located that their respective axes substantially extend in a single plane which intersects the center axis X of the housing; and the inner peripheral walls of the housing 1, composed of parts In and 1b, extendso closely around the spur gears '2, 3 and 4 that only the central gear 3 is surrounded by a ringshaped interspace 5 which serves for guiding the blind (inactive) currents of hydraulic medium passing tangentially and in counterfiow around the central gear. These currents are formed on the suction side as well as on the pressure side by the medium flowing between the two meshing locations of central gear 3 with the respective outer gears 2 and 4, and pass from the meshing region of mutually approaching teeth tothe region in whichthe gear teeth of the respective gears travel away from each other.

It has been found infeasible to utilize both delivering directions of the pump because in one direction of delivery the outer gear 4 is driven hydraulically with the effect that the sealing engagement between the gear-teeth flanks may become lost or unreliable. 'Utilizable in practice, therefore, is only'the control range of the central gear 3 in which the spacing of its gear axis from the driving spur gear 2 is equal or greater than the spacing between the respective axes of gears 3 and 4. Consequently, a single definite direction of delivery is correlated to a given direction of rotation'of the driving gear2 on shaft 6. Predicated upon this condition, it is anotherfeature of my invention to have the bores 7a, 7b for supplying and discharging the hydraulic medium communicate with the interior of the housing at respective locations that are close to the two sides respectively of the meshing engagement between the central gear and the free (i.e. entrained) outer gear 4, the latter gear being the one remote in the gear train from the driving gear 2. By virtue of this feature, a substantially complete separation of the active fluid flow from the blindor inactive fluid flow currents is effected so that the channel cross sections required for the blind current flow can be minimized. This promotes reducing the overall dimensions of the pump housing and also permits giving the interior pressure-loaded housing area a smallest possible size. The significance of this improvement will be realized by considering that the blind (inactive) current (flow quantity per unit time) amounts up to about of the active current delivered by the pump. I 7

Although by virtue of the above-described features of my invention the internal forces and the external dimensions of the pump housing are greatly reduced, there remains the fact that the lateral inner surface of the housing, particularly in the vicinity of the central gear 3, has large wall areas exposed to internal pressure. Despite the adjacent fastening bolts 1c of the housing, these wall areas constitute, in effect, two flexible diaphragms. Hence, the housing portions 1a, 117 must be given a relatively thick and heavy wall in order to prevent elastic deformation which may impair the efiicacy of the internal sealing gaps.

The same purpose, but with a smaller wall thickness and. weight of the housing is achieved according to another feature of my'invention described presently. As described above, the eccentric journalling member 9a for the central gear 3 is designed as, or provided with,

a hollow shaft 9. A bolt 8, passing with radial clearance through the shaft 9, is rigidly connected with the walls of the two housing portions 1a and 1b so as to constitute a rigid anchor which prevents elastic deflection of the two housing walls under the internal pressure of the pump. According to FIGS. 1 and 2, the bolts 8 is mounted on and between the housing portions 1a and 112 by means of 'a cover disc 10 and a pressure cap 11. The pressure cap surrounds the end of the shaft 9. protruding out of the housing portion 112. In this manner, the tensioning bolt Sis rigidly braced against the two housing portions, thus holding them rigidly together in opposition to any effects of internal pressure.

Such a tensioning bolt 8 is capable of withstanding the internal pressure of the hydraulic medium at a much smaller expenditure in material and weight than would be required by giving housing portions 111, 1b a correspondingly great thickness to prevent bending deformation. The bolt further affords the possibility of being tightened to a greater or lesser extent, thus permitting, in conjunction with the elasticity of the housing walls, and adjustment of the sealing gaps between the spur gears and the lateral housing surfaces within certain limits. Another advantage of the tensioning bolt 8 passing coaxially through the hollow shaft f the eccentric 9a is the fact thatthe pressure cap 11 can simultaneously be used for limiting the angular adjusting motion of the control shaft 9. To this end, the pressure cap 11 is nonrotatably secured to housing portion 1b by, means of a groove 12 and a pin 13. The pin is fastened in the housing and engages the groove, thus preventing the cap 11 from rotating relative to the housing. A peripheral slot 16 in cap 11 limits the angular motion of the control member Sawhose hub 15 has internal teeth parallel to the hub axis and in meshing engagement with corresponding teeth of the control shaft 9, thus transmitting any turning motion of member 8a to the shaft 9 and its eccentric journal portion 9a. The pressure cap 11 thus simultaneously forms the limit stops for control member 8a.

In principle, a tensioning bolt, like the one denoted by 8, may also be provided to pass through the driving shaft 6, in this case designed as a hollow shaft, of the driving outer gear 2. A corresponding tensioning bolt may also be provided to pass through the shaft 17 which in this case would have to be hollow, for the free outer gear 4. Such a tensioning bolt, denoted by 8b and passing through a hollow shaft 17 for the outer gear 4, is illustrated in FIGS. 3 and 5 as a feature of the second embodiment more fully described hereinafter. In practice, however, a tensioning bolt in the hollow drive shaft 6 for the driving outer gear 2 can be employed only with difficulty because the driving clutch or other driving member to be mounted on the protruding outer end of the shaft 6 would necessitate the provision of a relatively large pressure cap, and if the shaft 6 is to be coupled together with an axially aligned drive shaft, the provision of a pressure cup would virtually be infeasible. For that reason, it is preferable to journal a shaft 17 of the entrained outer gear 4 on a spacer bolt 8b tightened between the two housing portions as shown in FIG. 5.

Aside from providing for a very stiff connection between the two housing portions 1a, 1b (FIGS. 1, 2), a tensioning bolt 8 (or 8b) may simultaneously serve for facilitating an accurate mutual aligning and fixing of the two housing portions.

Another feature of my invention, contributing to further reducing the weight of the pump housing, is the following. In the conventional gear-type pumps, the housing is divided into two portions along a plane coincident with one lateral surface of the inserted spur gears so that one housing portion has relatively deep cavities for accommodating the spur gears as the other housing portion has a generally planar inner surface and constitutes essentially only a cover. With this conventional design, the contact forces of the gear journals in the housing portion forming the cover act as forces because of the here missing hydraulic relief, these displacing forces tending to cause relative displacement between the two housing portions. Such displacing forces, in a triple-gear controllable-displacement pump of the type with which the present invention concerns itself, attains an excessive magnitude even at moderate internal pressures. For that reason, the housing walls and the fastening screws between the housing portions would have to be made particularly rugged and stable. This, however, is contrary to the desired aim of reduction in housing weight. According to another feature of my invention, however, the plane of division between the housing portions, this plane being denoted by id in FIG. 2, is placed substantially in the center plane of the gear train, and both housing portions are provided with symmetrically equal cavities for accommodating the gears.

As a result, a symmetrical loading of both half-portions of the housing is secured and the displacing forces otherwise active in the divisional plane are eliminated, thus affording a reduction in weight of the housing as well as the fastening screws required for the housing. By virtue of the same feature, furthermore, the peripheral surface area subjected to the delivering pressure of a pump in each half portion of the housing possesses a smaller internal height and hence permits a reduced radial wall thickness of the housing for a given amount of stiffness.

For the purposes to be described presently, it is advantageous, according to another embodiment of the invention to place the plane of division between the two housing portions not accurately onto the center plane of the gear train, but to shift the plane of division somewhat away from the center plane while keeping the divisional plane still considerably spaced from the lateral surfaces of the gears. This feature will now be more fully described with respect to FIG. 5.

In conventional production, the manufacturer of a given pump type usually produces a series of such pumps which differ from each other by respectively different axial heights of the spur gears in order to permit using the same machine tools for fabricating the housings and gear teeth in the production of pumps suitable for respectively different delivering quantities. For this purpose, it has heretofore been necessary to produce for each given axial height of the gears a particular housing portion. For example, the manufacturer producing the same type of pump with gears of respectively different heights for three rated deliveries, has been compelled to produce a total of four different housing models, namely one cover portion, and three dilferent cavity portions. However, if, according to the last-mentioned feature of my invention, the divisional plane of the two housing portions is located away from the lateral gear surfaces in a location where the height of the gears is unequally divided, the number of housing models necessary for a given number of pumps having respectively different ratings is considerably reduced.

Thus, in the embodiment illustrated in FIG. 5, the divisional plane 20d of the two housing portions 20a, 20b is displaced somewhat toward the left of the gear center plane.

Only two models or types of housing portions are thus required for producing a pump housing according to FIG. 5 of various capacities, namely the model according to housing portion 20a and another model for housing portion 2017. However, these two types of housing portions permit being combined with gear grains of respectively diiferent axial heights so as to result in pumps for three different delivery ratings. For example, assume that the inner width of the housing portions 20a, 20b is 7 and 14 mm. respectively. With the aid of housing portions according to only these two models, the following total inner widths can readily be put together: 7+7=l4 mm., 7+l4=21 mm., and l4+l4=28 mm. If only one additional housing portion with, for example, 18 mm. inner width is added to the available models, the three models afford being assembled to housings having six different inner width magnitudes and correspondingly different delivery ratings. With the same number of three housing models, on the other hand, the conventional practice would permit obtaining only two different delivery ratings. Consequently, the asymmetrical subdivision of the housing according to the invention as just described greatly reduces the manufacturing costs of a series of pumps. The asymmetrical division of the housing somewhat affects the hydraulic compensation of the supporting forces acting in the journal openings or bearing portions of the housing, but only to a minor extent so that the remaining degree of compensation remains satisfactory.

The pump housing can be further improved with respect to compactness and light weight by the following features incorporated in the embodiment illustrated in FIGS. 3 to 11. In this pump, the interior walls of the housing are placed in close proximity not only to the outer gears 2, 4, but also to the central gear 3. That is, the interspace between the central gear 3 and the peripherally adjacent surface of the housing wall is kept so small that the central gear 3 is just capable of performing the necessary radial displacing motion. For the purpose of passing the blind (inactive) currents of hydraulic medium, the two housing portions 20a, 20b (FIGS. 5, 6, 7, 10) in this case are provided with grooves 21 which preferably extend beside the lateral surfaces of the spur-gear teeth and are of annular shape (FIGS. 4, 6, 7).

Such guiding channels 21 for the blind currents permit reducing the width of the housing to a minimum and simultaneously increasing the stiffness of the lateral housing walls to such an extent that for low up to medium pressures an additional tensioning bolt (8 in FIG. 2) passing through the control shaft 9 becomes unnecessary. Furthermore, such guiding channels for the blind currents also constitute the most favorable solution from the technical viewpoint of flow mechanics because the blind currents are mainly constituted by flow currents of hydraulic medium which are squeezed laterally out of the gear meshing space in the meshing zones of the gears, or by flow currents of medium which at the meshing location enter between the teeth, so that, for example, the guiding of the blind currents along the periphery of the central gear requires a considerably higher force in reversal of flow direction, thus involving greater eddycurrent losses. The diminution in the width of the housing, however, is not attained at the expense of a corresponding increase in axial height of the housing. As will be seen from FIG. 6, the wall portion surrounding the annular channels 21 are still located behind the outer planar surface of the journal hubs.

The provision of the lateral ring channels 21 for. the blind currents permits applying the following further improvement of the housing, not applicable when the blind currents are required to pass along the outer periphery of the central gear 3 according to FIG. 1. This improvement resides in the fact that a respective anchoring bolt 22 (FIGS. 3, 4), firmly interconnecting the two housing portions a and 20b, is located in each of the gusset or wedge-shaped areas formed by the peripheral surfaces of the spur gears near the range of their mutual meshing engagement. These bolts 22 are placed so closely to the apex of the wedge area that their spacing from the gear peripheries is not substantially greater than one half of the bolt diameter and preferably smaller than this dimension. The bolts 22 greatly improve the bracing of the lateral housing walls with respect to the static pressures in the housing caused by the hydraulic medium. The width of'the wall portions located between the bolts 22 and'subjected to bending stresses are greatly reduced, thus further contributing to the possibility of reducing the wall thickness and hence the weight of the housing. In general, the provision of the bolts. 22 as described above results in such a general diminution of the mutual spacing between the fastening screws of the housing structure, that the total number of the fastening bolts can be reduced without detriment to the strength of the housing. Thus, for example, a total of eleven fastening bolts 1c for connecting the two housing portions are used in the embodiment of FIGS. 1, 2, whereas only eight bolts .22 are needed in the embodiment of FIG. 3 and following without detrimental results.

The arrangement of the housing bolts 22 in the vicinity of the gear-meshing areas just described, is not compatible with the particular arrangement of the inlet and outlet ducts 7a, 7b for the hydraulic medium described above with reference to FIG. 1, if, as is usually desirable, these ducts are to extend parallel to the gear axes on the lateral sides of the pump housing, in which case these ducts would just be located at a point where a fastening bolt 22 is supposed to be mounted. However, to permit employing both advantageous features, it is preferable to arrange the inlet and outlet ducts 23 (FIG. 4) of the housing so as to extend in coaxial relation to respective bolts 22. The ends of the bolts 22 protruding out of the housing are preferably used for the attachment of accessory structures that permit a low-resistance delivery of the hydraulic medium into or out of the hydraulic lines to be attached to the pump.

The foregoing features are embodied in the pump according to FIGS. 3 through 10. Two elbows 25 (FIGS.

3, 7), serving as pressure and suction ducts, are fastened to the pump housing by means of respective tensioning bolts 22 (FIG. 7). Such elbows have the further advantage that they readily permit turning the flow direction of the incoming or outgoing hydraulic medium over a large angular range thus greatly facilitating the installation of the pump in many cases. Another advantage is the fact that the housing need not be provided with a screw thread for fastening the duct members or other conduits, thus preventing the danger that the housing may become distorted when screwing the duct members or other conduits directly into the housing.

FIGS 8 and 9 illustrate a modified design of the connecting duct members that are attached to the machine housing by means of respective bolts 22 and can be used in lieu of the duct members 25 illustrated in FIGS. 3 and 5 when it is desired to have the incoming and on"- tationally adjustable elbows 25 according to FIGS. 3

and 7, with respect to the fastening of the duct members to the housing-by means of the bolts 22. However, the

duct members 38 according to FIG. it) constitute a double elbow so as to permit extending the hydraulic lines in a direction parallel to the axis of the fastening bolt 22, while also permitting a radial displacement of turning the duct structure 38 about its fastening bolt.

If deseired, the bolt 22 for fastening the housing portions together and for attaching the. duct members to the front side of the pump housing may be firmly joined with the rearportion of the housing by having the bolts in direct threaded engagement with a bore in the rear housing wall. However, it is preferable to provide for the versatility achievable by combining different housing portions in order to obtain pumps of respectively different delivery rating, and to achieve this end by making the housing portions at the front and rear of the housing as much identical as possible. For that reason, the embodiment of FIGS. 3, 4, 5, 7 and 10 has the rear portion 200: provided with the same bores 23 (FIG. 10) and annular shoulders that are provided in the front portion 20b for seeking, centering and attaching the duct members. In this case, the rear end of the bolts 22' may pass through a cover and sealing disc 27 (FIG. 10) or,

according'to FIGS. 5 and 7, may also serve to attach to the housing an over-pressure valve 24 in hydraulic cornmunciation between the pressure and suction chambers of the pump.

If, as just described, the front and rear portions of the housing are provided with the same bores 23, it is readily possible to locate the inlet and outlet ducts and duct members of the pump on one or the other side of 'the housing. For the same reason, the suction line can readily be connected to one side of the housing and the pressure line to the opposite side.

Another essential advantage obtained by virtue of identical bores 25 in both housing portions is the following. As mentioned above, the triple-gear pump of controllable displacement is to be operated for only one given direction of delivery which is dependent upon the direction of rotation of the drive shaft 6 (FIG. 1, 5). By virtue of the fact that according to the above-described features,

'the two housing portions are of greatly Similar design,

not only the duct members for supplying and discharging the hydraulic medium, but also the driving gear 2 with its shaft 6 (for example, as shown in FIG. 5) can be inserted selectively so that the shaft'end and the control shaft 9 protrude toward the left or toward the right from the housing. This permits adapting a pump, without any other structural change, to any desired correlation of the driving direction, position of the driving shaft, position of the control shaft, or the duct connections, simplyby reversing'the proper component parts of the pump.

As mentioned above, it is among the objects and advantages of my invention to reduce the internal frictional losses of the pump which are significant with triplegear controllable-displacement pumps because of the relatively large sealing gaps which separate the pressure space from the suction space during operation. This re duction of internal friction and the resulting increase in efficiency of the pump can be further improved by providing grooves in both housing portions which extend in the planar inner housing surfaces that are travelled over by the teeth of the two outer spur gears 2 and 4 (FIG. 4, 5, 11). These grooves are about 0.3 to 0.5 mm. deep. They commence from the suction chamber of the pump and extend transversely to the main middle axis X of the pump (FIG. 4) over an additional angular range of approximately ti=45 toward the pressure zone of the housing. It has been found in practice that such grooves result in a considerable reduction of the frictional losses and hence also of the heating of the hydraulic medium.

Also, for the purpose of reducing friction and in accordance with a further feature of my invention, the ring-shaped planar housing surfaces 29, 30, 31 (FIGS. 4, 6, 7, and 11) which are in sealing engagement with the spur gears 2, 3, 4 are provided with a radial groove 32 of approximately 0.2 to 0.5 mm. depth. This groove is located on the suction side of the pump, extending approximately normal to the main middle axis X of the housing. The radial grooves 32 operate to lubricate the lateral surfaces of the spur gears even under zeropressure operation at high rotating speeds, and they simultaneously lubricate the gear bearings with increased reliability.

Further features of my invention, embodied in the machines already described above, relate to the objects of minimizing the operating noise. Such noise may be due to two causes.

First cause: A very rapid increase in pressure from suction to delivering pressure occurs in the gap between the gear teeth travelling from the suction chamber to the pressure chamber of the pump housing. This causes noise-generating oscillations in the housing structure as well as in the hydraulic medium of the pressure space.

This first source of noise is minimized according to the invention by means of noise reducing recesses 33 (FIGS. 4, 11) machined into both housing portions. These recesses 33 are located in the vicinity of the spur gear whose teeth travel toward the pressure space (this being the upper gear 4 in FIG. 4). The recesses 33 are machined into the planar surfaces of this gear, and extend from the pressure chamber up to a horizontal center line which is normal to the X axis of the housing and intersects the upper journalling bore of the housing. The depth of the recesses 33 need only be slight and can be determined by testing. By virtue of these recesses, the gaps between the gear teeth that are under suction pressure enter into a throttling hydraulic connection with the pressure chamber prior to actually entering into this chamber. These throttling connections of the hydraulic medium through the recesses 33 have the ettect that the gaps between the intermeshing teeth can gradually become loaded up to the delivering pressure, thus reducing or virtually eliminating the pressure shocks that cause the noise-generating oscillations.

Second cause: The second cause for excessive noise is undesired pressure of the medium in the gaps between the meshing gear teeth. One of the most difficult tasks of noise reduction in such displacement-controllable gear pumps is the reduction of a squeezing action imposed upon the hydraulic medium within the tooth gaps. Of similar importance for noise reduction is the requirement that no excessive negative pressure be permitted to develop between the intermeshing gaps as they move out of engagement with each other, because such excessive negative pressure may result in considerable oscillations within the suction line and may also produce cavitation phenomena. In the conventional gear pumps of the general type, having a constant volumetric delivery, various structural expedients serving the just-mentioned purpose have become known, but these cannot be employed in controllable triple-gear pumps of the type here concerned, because in triple-gear pumps the meshing degree of the gear teeth is not fixed but, depending upon the adjusted rate of delivery, varies from the value 1.0 up to beyond the value 2.0. Furthermore, the operating conditions of i the intermeshing gears in controllable displacement gear pumps are also fundamentally different from those of normal fixed-delivery pumps, in that the teeth-flank engagement, depending upon the adjusted rate of delivery, changes from approximately zero up to an unusually great value.

Thorough investigation has ultimately resulted in the novel recesses 35a, 35b, 35c and 35d in the interior planar surfaces of the housing and in the vicinity of the two meshing regions having a shape as illustrated in FIGS. 12 and 13 by heavy lines, these recesses being identified in FIGS. 12 and 13 by horizontal hatching. FIG. 12 illustrates the teeth in and 3a of the respective spur gears 2 and 3 (corresponding to those of FIGS. 2 and 5). FIG. 13 identifies the teeth 3a and 4c of respective gears 3 and 4 (corresponding to those of FIGS. 2 and 5) by light weight lines. In both illustrations 12 and 13, the two gears are shown in meshing relation to each other. FIG. 12 relates to a setting in which the teeth of the respective gears 2, 3 occupy positions corresponding to the greatest possible spacing between the axes of the respective gears. In contrast thereto, FIG. 13 shows the meshing teeth of gears 3, 4 for the smallest possible spacing of the respective axis, but with clearance between the teeth flanks. in both illustrations, the pressure-loaded teeth flanks are identified by arrows. The two illustrations are correlated to each other. That is, they correspond to the conditions obtaining in a triplegear controllable-displacement pump adjusted to its available maximum delivery. For example, FIGS. 12 and 13 may relate to the gear trains of the pumps illustrated in FIG. 2 and FIG. 4, respectively. The direction of gear rotation in FIGS. 12 and 13 corresponds to that of the respective gears as indicated by directional arrows in PEG. 4.

It will be remembered that according to the invention the pump is to be designed only for operation in a given direction of delivery and consequently for a given rotational direction of the driven out spur gear 2. Accordingly, the flank engagement of the teeth takes place only along the straight lines E and E of force transmission which are indicated in FIGS. 12 and 13 and which intersect the center axis X at an angle of a and at 90a respectively. To prevent squeezing of the hydraulic medium in the tooth gaps, these gaps, during meshing operation, are to remain in hydraulic connection with the suction chamber (FIGS. 4, 12) or the pressure chamber (FIGS. 4, 13) of the pump, until the space enclosed by the force-transmitting flanks possesses its smallest volume, this flank-enclosed space being identified in FIGS. 12 and 13 by diagonal hatching. This minimum volume of the inter-flank space is practically attained when the distance defined by the force-transmitting flanks along the line E or E is bisected into equal half distances by the main center axis X of the pump housing (see FIGS. 1, 4, 12 and 13). This is just the case with the position of the meshing gears as illustrated in FIGS. 12 and 13. For avoiding an undesired negative pressure in the inter-tooth spaces Q1 and Q2 enclosed by the flanks, these spaces, immediately after attaining minimum volume, are to be placed into hydraulic communication with the hydraulically-opposite delivering space of the pump. That is, in the example of FIG. 12 the space Q1, upon attaining its minimum volume, is to be placed into communication with the pressure space of the pump; and in the example or" FIG. 13, the corresponding space Q2, upon attaining its minimum volume, is to be hydraulically connected with the suction space of the pump, so that the enclosed inter-teeth volume, which increases during further rotation, can readily be replenished with hydraulic medium through the then established communications.

Based upon the above-presented concepts, and in accordance with my invention, I have arrived at the particular design of the housing wall within the meshing zones at the pump gears as are shown by heavy lines in FIGS.

12 and 13. As mentioned, the inner walls of each housing portion, such as portion 20a, are provided on both sides of each meshing range of mutually engaging gears, with recesses 35a, 35b, 35c and 35d whose contour and shape are emphasized in both illustrations by horizontal hatching. Due to these recesses, the planar housing surfaces which are in intimate face-to-face contact with the lateral surfaces of the teeth to provide proper sealing, are reduced to the shape of a sealing bridge B1 or B2. This bridge follows substantially the line E or E of the active forces and has a link only slightly in excess of the distance along the action line E E identifying the distance along which the teeth of the respective gears are in meshing contact with each other. The bridge areas B1, B2 of the planar housing surfaces are further so shaped on both sides of the center axis X, that when the teeth are in the position at which two tooth gaps together define a minimum of enclosed volume Q1, or Q2, the tooth-flank contours enclosing this volume approaching each other a minimum distance or to such an extent that a relatively slight departure of the tooth position from this neutral position establishes the desired bydraulic connection of the tooth gap pairs with the suction or pressure space of the pump.

I am aware of the fact that the provision of recesses in the innerwalls of a gear-pump housing has already become known for similar purposes (US. Patent No. 2,354,992, German Patent No. 366,152). However, in both known cases, it was presumed that the teeth engage each other virtually Without clearance and that no change in spacing between the gear axes takes place. The particular shaping of the recesses 35a to 35d according to the present invention, for supplying or removing hydraulic medium from the areas at the lateral surfaces of the gear teeth within the meshing range, takes into account the change in spacing between the gear axis for carrying into controllable triple-gear pumps, and for that purpose is designed in consideration of the change in value occurring between two mutually communicating tooth gaps of the respective gears.

The above-described design of the recesses in the planar housing wall for supplying and removing medium I in the meshing range of the gear teeth results in a considerable reduction of the operating noise. A further improvement in the same sense is obtained if care is taken that the abrupt change in pressure in the tooth gaps travelling from the suction to the pressure side and vice versa is somewhat moderated. Accordingly, it is another feature of my invention, embodied in the devices illustrated and already described, to give the recesses 35a, 35c (FIGS. 12, 13) in the range'of the teeth that enter into meshing engagement or out of such engagement on the suction side of the pump, a contour shape similar to the contour of the adjacent two flanks of the teeth located in neutral position, so that these recesses approach the flanks of the latter teeth only up to a given distance a. As a result, some amount of pro-compression is imparted to the hydraulic medium enclosed in the tooth-gap pairs travelling from the suction space to the pressure space, and some degree of expansion is permitted to the hydraulic medium enclosed in the tooth-gap pairs travelling from the pressure space to the' suction space after passing through the neutral position. Such compression or expansion then effects the desired smoother and hence less noisy change in pressure within the enclosed volumes between the tooth-gap pairs.

It may again be emphasized that a controllable-displacement pump of the type herein described can find use in actual practice only if its above-described particular deficiencies and disadvantages are greatly minimized or eliminated. This purpose is served by all above-described features relating to a pump housing according to my invention. It is not necessary in a given pump of this type to simultaneously employ all features, but it may from case l2 to case be preferable to employ ditferent combinations of these features to obtain best technological results.

For example, the housing of controllable-displacement triple-gear pumps, may be composed of three instead of two parts and particularly if the pump is to be particularly suitable for high delivering pressures. In this case, the housing may comprise a middle portion around the gear teeth, and two cover portions. In this case, too, the above-described features of my invention are readily applicable with the exception of those relating to the particular position of the divisional plane in a two-part housing.

Some of the features of my invention, for example the novel separation of the housing in the range of approximately one half of the axial gear height,'and the provision of the fastening screws for the housing portions within the wedge-shaped rangebetween the peripheries of each two meshing gears, as well as the fastening of the duct members without any'further engagement with the housing proper, by means of the just-mentioned fastening bolts, are applicable also for gear pumps of a type other than those particularly disclosed herein.

'Such and other modifications will be obvious to those skilled in the art upon a study of this disclosure and without departing from the essential features of my invention as set forth in the claims annexed hereto.

I claim:

1. A controllable-displacement hydraulic machine comprising a train of at least three spur gears for displacing hydraulic'medium including an intermediate gear and two outer gears meshable therewith, a housing for said gears having two component portions Whose separating surface is located in a plane which divides the gear teeth within the axial thickness of said gears, said housing being provided with a plurality of journalling locations forthe respective gears so arranged that the respective gear axes are located substantially in a single plane passing through the axes of said outer gears, the peripheral wall surfaces of said housing extending closely about each of said two outer gears and being spaced from the non-meshing portion of said intermediate gear and extending beside the lateral surface of the teeth of said intermediate gear so as to form a ring-shaped hollow space adjacent said non-meshing portion of said intermediate gear forthe guidance of blind hydraulic currents formed to cause said blind currents to passtangentially and in counterfiow about said intermediate. gear, drive means connected to one of said outer gear, means for radially displacing said intermediate gear and the respective journalling location for said intermediate gear being located so that the spacing of the axis of said interme diate gear from the axes of said two outer gears is variable continuously and only in a range wherein the spacing of the intermediate gear axis from the axis of said one outer gear is always 'at least as great as the spacing between said intermediate gear axis and the axis of the other ,of said two outer gears, said housing being provided with supply and discharge ducts for input and output of hydraulic medium, said respective ducts being located in said housing on mutually opposite sides of said plane passing through the axes of said outer gears, said ducts communicating with the interior of said housing in the vicinity of the area where said intermediate gear meshes with said other gear, said means for displacing the intermediate gear comprising a control shaft mounted in said housing and coaxial with said intermediate gear for journalling and radially displacing the latter, a control member connected to said control shaft to control the radial displacement of said intermediate gear, fastening means coaxial with said control shaft for fastening said two housing portions together, structural bracing means for supporting and fastening means against the external surfaces of the respective housing portions, said bracing means comprising a pressure cap which extends about the end of said control shaft, said pressure cap being provided with a recess through which said control member passes from said control shaft to the outside, said recess serving for limiting the angular range of displacement of said control member, said housing conforming to the outer periphery of said intermediate gear so closely that the latter can perform only its necessary radial displacing motion, said ring-shaped hollow space including channels adjacent to lateral surfaces of at least said intermediate gear, said channels being located in both of said two housing portions for guiding blind fiow currents of hydraulic medium.

2. A contr-ollable-displacement hydraulic machine comprising a train of at least three spur gears for displacing hydraulic medium including an intermediate gear and two outer gears meshable therewith, a housing for said gears having two component portions whose separating surface is located in a plane which divides the gear teeth within the axial thickness of said gears, said housing being provided with a plurality of journalling locations for the respective gears so arranged that the respective gear axes are located substantially in a single plane passing through the axes of said outer gears, the peripheral Wall surfaces of said housing extending closely about each of said two outer gears and being spaced from the non-meshing portion of said intermediate gear and extending beside the lateral surface of the teeth of said intermediate gear so as to form a ring-shaped hollow space adjacent said non-meshing portion of said intermediate gear for the guidance of blind hydraulic currents formed to cause said blind currents to pass tangentially and in counterflow about said intermediate gear, drive means connected to one of said outer gears, means for radially displacing said intermediate gear and the respective journalling location for said intermediate gear being located so that the spacing of the axis of said intermediate gear from the axes of said two outer gears is variable continuously and only in a range wherein the spacing of the intermediate gear axis from the axis of said one outer gear is always at least as great as the spacing between said intermediate gear axis and the axis of the other of said two outer gears, said housing being provided with supply and discharge ducts for input and output of hydraulic medium, said respective ducts being located in said housing on mutually opposite sides of said plane passing through the axes of said outer gears, said ducts communicating with the interior of said housing in the vicinity of the area where said intermediate gear meshes with said other gear, a control shaft mounted in said housing and coaxial with said intermediate gear for journalling and radially displacing the latter, a control member connected to said control shaft to control the radial displacement, fastening means coaxial with said control shaft for fastening said two housing portions together, structural bracing means for supporting said fastening means against the external surfaces of the respective housing portions, said bracing means comprising a cover disc and a pressure cap which extends about the end of said control shaft, said pressure cap having a groove, a pin fastened in said housing and engageable with said groove to prevent said pressure cap from rotating, said cap being further provided with a recess through which said control member passes from said control shaft to the outside, said recess serving for limiting the angular range of displacement of said control member, said two housing portions having symmetrically the same shape, the plane of division between said two housing portions being located approximately at one half of the axial thickness of at least said one gear, each housing portion having respective mounting means for mounting said drive means, said control shaft and for connecting input and output lines for hydraulic medium, said respective mounting means being so positioned on each housing that said drive means, said control shaft as well as said input and output lines can be selectively attached on either housing portion to accommodate right hand and left hand installations.

3. A controllable-displacement hydraulic machine comprising a train of at least three spur gears for displacing hydraulic medium including an intermediate gear and two outer gears meshing therewith, a housing for said gears having two component portions whose separating surface is located in a plane which divides the gear teeth within the axial thickness of said gears, said housing being provided with a plurality of journalling locations for the respective gears so arranged that the respective gear axes are located substantially in a single plane passing through the axes of said outer gears, the peripheral wall surfaces of said housing extending closely about each of said two outer gears and being spaced from the non-meshing portion of said intermediate gear and extending beside the lateral surfaces of the teeth of said intermediate gear so as to form a ring-shaped hollow space adjacent said non-meshing portion of said intermediate gear for the guidance of resulting blind hydraulic currents to cause said currents to pass tangentially and in counterflow about said intermediate gear, drive means connected to one of said outer gears, means for radially displacing said intermediate gear, and the respective journalling location for said intermediate gear being located so that the spacing of the axis of said intermediate gear from the axes of said two outer gears is variable continuously and only in a range wherein the spacing of the intermediate gear axis from the axis of said one outer gear is always at least as great as the spacing between said intermediate gear axis and the axis of the other of said two outer gears, the peripheries of said intermeshing three gears forming respective gusset-shaped spaces near the region of meshing engagement, fastening means traversing said gusset-shaped spaces and connecting said housing portions together, said fastening means being located so close to the apex of the respective gusset space that the distance of the respective fastening means from the closest gear periphery is not greater than one half the diameter of the fastening means, said housing having connecting duct members for connection with hydraulic-medium lines for supplying and removing the hydraulic medium, said duct members extending in coaxial relation to respective ones of said fastening means located in the gusset-shaped spaces adjacent to the meshing regions of the gears, a pressure-limit valve forming a communication between the duct members, said valve being mounted on said housing and attached thereto by said fastening means.

4. A controllable-displacement hydraulic machine comprising a train of at least three spur gears for displacing hydraulic medium including an intermediate gear and two outer gears meshing therewith, a housing for said gears having two component portions whose separating surface is located in a plane which divides the gear teeth within the axial thickness of said gears, said housing being provided with a plurality of journalling locations for the respective gears so arranged that the respective gear axes are located substantially in a single plane passing through the axes of said outer gears, the peripheral wall surfaces of said housing extending closely about each of said two outer gears and being spaced from the non-meshing portion of said intermediate gear and extending beside the lateral surfaces of the teeth of said intermediate gear so as to form a ring-shaped hollow space adjacent said non-meshing portion of said intermediate gear for the guidance of resulting blind hydraulic currents to cause said currents to pass tangentially and in counter-flow about said intermediate gear, drive means connected to one of said outer gears, means for radially displacing said intermediate gear, and the respective journalling location for said intermediate gear being located so that the spacing of the axis of said intermediate gear from the axes of said two outer gears is variable continuously and only in a range wherein the spacing of the intermediate gear axis from the axis of said one outer gear is always at least as great as the 15 spacing between said said intermediate gear axis and th axis of the other of said two outer gears, said housing forming respective suction andpressure chambers together with at least one of said gears, and said two housing portions having internal planar surfaces laterally adjacent to the teeth of said two outer gears, each of said housing portions being provided with said'ringshaped spaces, the latter being located in said planar housing surfaces, said recesses extending from the wall of said housing forming said suction chamber to the maincenter axis of said housing and extending from the latter axis by an additional amount of 45 toward said pressure chamber, and said housing being provided with supply and discharge ducts for input and output of hydraulic medium, said respective ducts being located in said housing on mutually opposite sides of said plane passing through the axes of said outer gears, said ducts communicating withrespective suction and pressure chambers in the vicinity of the area where saidintermediate gear meshes with said other gear.

5. A controllable-displacement hydraulic machine comprising a train of at least three spur gears for displacing hydraulic medium including an intermediate gear and two outer gears meshing therewith, a housing for said gears having two component portions whose separating surface is locatedin a plane which divides the gear teeth within the axial thickness of said gears, said housing being, provided with a plurality of journalling locations for the respective gears so arranged that the respective gear axes are located substantially in a single plane passing through the axes of said outer gears, the peripheral wall surfaces of said housing extending close- 1y about each of said two outer gears and being spaced from the non-meshing portion of said intermediate gear and extending beside the lateral surfaces of the teeth of said intermediate gear so as to form a ring-shaped hollow space adjacent said non-meshing portion of said intermediate gear for the guidance of resulting blind by draulic currents to cause said currents to pass tangentially and in counter-flow about said intermediate gear, drive means connected to one of said outer gears, means for radially displacing said intermediate gear and the respective journalling location, said intermediate gear being located so that the spacing of the axis of said intermediate gear from the axes of said two outer gears is variable continuously and only in a range wherein the spacing of the intermediate gear axis from the axis of said one outer gear is always at least as great as the spacing between said intermediate gear axis and the axis of the other of said two outer gears, the peripheries of the said three intermeshing gears forming respective gusset-shaped spaces near the region of meshing engagement, saidhousing having internal planar surfaces later-ally adjacent to the teeth of at least two of said gears, and being shaped to form respective suction and pressure chambers together with at least one of said gears and comprising said two housing portions, fastening means traversing each of said gusset-shaped spaces for connecting said housing portions together, said fastening means being located so close to the apex of the respective gusset space that the distance of the respective fastening means from the closest gear periphery is not greater than one half the diameter of the fastening means, said duct members extending in coaxial relation to respective ones of said fastening means located in the gusset-shaped spaces adjacent to the meshing regions of the gears, each of said housing portions being provided with said ringshaped spaces, the latter being located in said planar housing surfaces, said recesses extending from the wall of said housing forming said suction chamber to the main center axis of said housing and extending from the latter axis by an additional amount of 45 toward said pressure chamber, each of said internal planar surfaces being in sealing engagement with said lateral surfaces of said two gears and each surface having a radial groove locatedon the suction Side of the machine and extending 16 approximately normal to the main center axis of said housing, eachof said grooves extending radially from the respective gear journalling location of said housing up to the respective ring-shaped recess.

6. A machine according to claim 1, the peripheries of intermeshing gears of 'said plurality of gears forming respective gusset-shaped spaces near the region of their meshing engagement, respective fastening means traversing each of said gusset-shaped spaces for connecting said housing portions'together, said fastening means being located so close to the apex of the respective gusset space that the distance of the respective fastening means from the closest gear periphery is not greater than one half the diameter'of the respective fastening means.

'7. In a machine according to claim 6, said respective fastening means comprising a tensioning bolt, a total of not more than eight of said tensioning bolts being required for fastening the housing portions together.

8. In a machine according to claim 6, said housing having connecting duct members for connection with hydraulic-medium lines for supplying. and removing the hydraulic medium, said duct members extending in coaxialrelation to respective onesof saidfastening means located in' the gusset-shaped spaces adjacent to the meshing regions of the gears, said duct members being attached by said fastening means to the housing.

9. A controllable-displacement hydraulic machine comprising a train of at least three spur gears for displacing hydraulic medium including an intermediate gear and two outer gears meshable therewith, a housing for said gears having two component portions whose separating surface is located in a plane which divides the gear teeth within the axial thickness of said gears, said housing being provided with a plurality of journalling locations for the respective gears so arranged that the respective gear axes are located substantially in a single plane passing through the axes of said outer gears, the peripheral wall surfaces of said housing extending closely about each of said two outer gears and being spaced from the non-meshing portion of said intermediate gear andextending beside thelateral surface of the teeth of said intermediate gear so as to form a ring-shaped hollow space adjacent said non-meshing portion of said intermediate gear for the guidance of blind hydraulic currents formed to cause said blind currents to pass tangentially and in counterflow about said intermediate gear, drive means connected to one of said outer gears, means for radially displacing said intermediate gear and the respective journalling location for said intermediate gear being located so that the spacing of the axis of said intermediate gear from the axes of said two outer gears is variable continuously and only in .a range wherein the spacing of the intermediate gear axis from the axis of said one outer gear is always at least as great as the spacing between said intermediate gear axis and the axis of the other of said two'outer gears, said housing being provided with supply and discharge ducts for input and output of hydraulic medium, said respective ducts being located in said housing on mutually opposite sides of said .plane passing through the axes of said outer gears, said ducts "communicating with the interior of said housing in the vicinity of the area where said intermedate gear meshes with said other 'gear, a control shaft mounted in said housing and coaxial with said intermediate gear for journalling and radially displacing the latter, a control member connected to said control shaft to control the radial displacement, fastening means coaxial with said control shaft for fastening said two component housing portions together, structural bracing means for supporting said fastening means against the external surfaces of therespective housing portions, said bracing means comprising a cover disc and a pressure cap which extends about the end of said control shaft, said pressure cap having a groove, a pin fastened in said housing and en- 17 from rotating, said cap being further provided with a recess through which said control member passes from said control shaft to the outside, said recess serving for limiting the angular range of diplacement of said control member.

10. In a hydraulic machine according to claim 9, the peripheral surfaces of said intermediate gear and said other outer gear defining together wedge-shaped areas within said housing, spacer bolt means located within said wedge-shaped areas for rigidly connecting said housing portions with each other and for journalling said other outer gear.

References Cited in the file of this patent UNITED STATES PATENTS 237,764 Medden Feb. 15, 1881 884,812 Gillmor et a1. Apr. 14, 1908 1,129,090 Hawley Feb. 23, 1915 1,287,118 Shore Dec. 10, 1918 18 Bechler Oct. 12, 1926 Wilkin Mar. 7, 1939 McIntyre Jan. 23, 1942 Gottlieb Aug. 1, 1944 Egersdorfer Aug. 14, 1945 Grosser Dec. 28, 1948 Cook Feb. 1, 1949 Rorive Apr. 17, 1951 Crosby Apr. 24, 1 951 Hedman June 22, 1954 Newrnier Feb. 19, 1957 Mosbacher Aug. 6, 1957 Murray et al June 23, 1959 Payne et a1 Dec. 20, 1960 Edwards et .al Apr. 18, 1961 Chrzanowski et a1. May 30, 1961 FOREIGN PATENTS Great Britain May 9, 1940 France May 19, 1959 

1. A CONTROLLABLE-DISPLACEMENT HYDRAULIC MACHINE COMPRISING A TRAIN OF AT LEAST THREE SPUR GEARS FOR DISPLACING HYDRAULIC MEDIUM INCLUDING AN INTERMEDIATE GEAR AND TWO OUTER GEARS MESHABLE THEREWITH, A HOUSING FOR SAID GEARS HAVING TWO COMPONENT PORTIONS WHOSE SEPARATING SURFACE IS LOCATED IN A PLANE WHICH DIVIDES THE GEAR TEETH WITHIN THE AXIAL THICKNESS OF SAID GEARS, SAID HOUSING BEING PROVIDED WITH A PLURALITY OF JOURNALLING LOCATIONS FOR THE RESPECTIVE GEARS SO ARRANGED THAT THE RESPECTIVE GEAR AXES ARE LOCATED SUBSTANTIALLY IN A SINGLE PLANE PASSING THROUGH THE AXES OF SAID OUTER GEARS, THE PERIPHERAL WALL SURFACES OF SAID HOUSING EXTENDING CLOSELY ABOUT EACH OF SAID TWO OUTER GEARS AND BEING SPACED FROM THE NON-MESHING PORTION OF SAID INTERMEDIATE GEAR AND EXTENDING BESIDE THE LATERAL SURFACE OF THE TEETH OF SAID INTERMEDIATE GEAR SO AS TO FORM A RING-SHAPED HOLLOW SPACE ADJACENT SAID NON-MESHING PORTION OF SAID INTERMEDIATE GEAR FOR THE GUIDANCE OF BLIND HYDRAULIC CURRENTS, FORMED TO CAUSE SAID BLIND CURRENTS TO PASS TANGENTIALLY AND IN COUNTERFLOW ABOUT SAID INTERMEDIATE GEAR, DRIVE MEANS CONNECTED TO ONE OF SAID OUTER GEAR, MEANS FOR RADIALLY DISPLACING SAID INTERMEDIATE GEAR AND THE RESPECTIVE JOURNALLING LOCATION FOR SAID INTERMEDIATE GEAR BEING LOCATED SO THAT THE SPACING OF THE AXIS OF SAID INTERMEDIATE GEAR FROM THE AXES OF SAID TWO OUTER GEARS IS VARIABLE CONTINUOUSLY AND ONLY IN A RANGE WHEREIN THE SPACING OF THE INTERMEDIATE GEAR AXIS FROM THE AXIS OF SAID ONE OUTER GEAR IS ALWAYS AT LEAST AS GREAT AS THE SPACING BETWEEN SAID INTERMEDIATE GEAR AXIS AND THE AXIS OF THE OTHER OF SAID TWO OUTER GEARS, SAID HOUSING BEING PROVIDED WITH SUPPLY AND DISCHARGE DUCTS FOR INPUT AND OUTPUT OF HYDRAULIC MEDIUM, SAID RESPECTIVE DUCTS BEING LOCATED IN SAID HOUSING ON MUTUALLY OPPOSITE SIDES OF SAID PLANE PASSING THROUGH THE AXES OF SAID OUTER GEARS, SAID DUCTS COMMUNICATING WITH THE INTERIOR OF SAID HOUSING IN THE VICINITY OF THE AREA WHERE SAID INTERMEDIATE GEAR MESHES WITH SAID OTHER GEAR, SAID MEANS FOR DISPLACING THE INTERMEDIATE GEARS COMPRISING A CONTROL SHAFT MOUNTED IN SAID HOUSING AND COAXIAL WITH SAID INTERMEDIATE GEAR FOR JOURNALLING AND RADIALLY DISPLACING THE LATTER, A CONTROL MEMBER CONNECTED TO SAID CONTROL SHAFT TO CONTROL THE RADIAL DISPLACEMENT OF SAID INTERMEDIATE GEAR, FASTENING MEANS COAXIAL WITH SAID CONTROL SHAFT FOR FASTENING SAID TWO HOUSING PORTIONS TOGETHER, STRUCTURAL BRACING MEANS FOR SUPPORTING AND FASTENING MEANS AGAINST THE EXTERNAL SURFACES OF THE RESPECTIVE HOUSING PORTIONS, SAID BRACING MEANS COMPRISING A PRESSURE CAP WHICH EXTENDS ABOUT THE END OF SAID CONTROL SHAFT, SAID PRESSURE CAP BEING PROVIDED WITH A RECESS THROUGH WHICH SAID CONTROL MEMBER PASSES FROM SAID CONTROL SHAFT TO THE OUTSIDE, SAID RECESS SERVING FOR LIMITING THE ANGULAR RANGE OF DISPLACEMENT OF SAID CONTROL MEMBER, SAID HOUSING CONFORMING TO THE OUTER PERIPHERY OF SAID INTERMEDIATE GEAR SO CLOSELY THAT THE LATTER CAN PERFORM ONLY ITS NECESSARY RADIAL DISPLACING MOTION, SAID RING-SHAPED HOLLOW SPACE INCLUDING CHANNELS ADJACENT TO LATERAL, SURFACES OF AT LEAST SAID INTERMEDIATE GEAR, SAID CHANNELS BEING LOCATED IN BOTH OF SAID TWO HOUSING PORTIONS FOR GUIDING BLIND FLOW CURRENTS OF HYDRAULIC MEDIUM. 